Many present scanners utilize tungsten light or other sources of white light. Colored or interference filters are usually used to produce monochromatic light. Fixed or adjustable slits produce a light beam of controlled width for scanning. Methods of separation, such as paper electrophoresis has improved greatly. Disc electrophoresis or isoelectric focusing has sharp resolution. The stained protein bands resolved by these techniques produces a complex pattern of closely stacked bands. Conventional scanners do not have compatible resolution for quantitative determination. Adjacent bands fuse together upon scanning.
Finer resolution is mainly obtained by utilizing a thinner light beam to scan with. A thinner light beam is produced by narrowing the slit that produces the beam. When the slit width gets to 0.10 millimeters or less the emerging beam produced by the slit diverges and the beam is wider than the slit. This limits the resolution of conventional scanners utilizing a white light source and a slit system to produce a thin light beam.
Using the phenomenom of laser, either the sharp edge or the filter technique produces a line laser of adjustable intensity. A segment of this line laser is taken and focused to a thinner beam by utilizing a cylindrical lens or mirror.